Devicter Relay 1 Node V1.0 (ATmega 328) – with support OTA update

Customer Reviews

Very interesting device, but with safety concerns. Review by Thomas

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This device is a great idea, I think, with a lot of nice functionality. I would love to use it in some of my projects.
Therefore I tried to dig for some more information, even on the linked blog. With limited success. My Russian is … well … limited.
I ended up with some safety concerns, unfortunately.
With having job background in electronics and product safety, I think the device does not include sufficient protection against electric shock. All advanced countries in the world have standards enforced that give minimal requirements regarding electric safety, e.g. IEC 60950 or IEC 60065. One of the important requirements is sufficient separation (insulation) of dangerous high voltage levels from areas that might be accessible by users. I think everybody understands why such safety requirements exist.
Just from seeing the wiki pictures of the device PCB and circuit diagram, the following problems are quite obvious:

1) The separation of the mains voltage part in the device (so called primary circuits, marked with "hot" on the device PCB) is NOT sufficient separated from the other circuitry. Since this other circuitry is quite likely to become user accessible (through sensors, actuators, buttons, indicators, ...) this is a problem.
2) There are no any information about the safety of the used AC-DC converter.
3) The device should have a over current protection, a suitable fuse.

Some explanations:
1) There are minimal values (according to applicable law-like standards) for distances between mains circuitry and secondary circuits. The details are a bit complicated because depending on mains voltage, maximal elevation of intended use, etc.
Simplified you can say, for 230V mains voltage, everything below 4.0 mm distance (through air) and 5 mm creepage (along surfaces) is not OK. By taking just the (unscaled) PCB picture, I would say the creepage is zero point something millimeter below D1. But other traces and components are too close to the “hot” zone as well.
This is a major design flaw.
2) I'm quite sure the AC-DC converter block has no safety approval (UL, SGS, GOST, TUV, CB or whatever). Nothing is known about the separation (insulation) of primary and secondary circuitry in that block or the transformer wiring insulation. Nothing is known about possible risks of insulation break-down due to overheating. I saw too many quick-and-dirty stuff in my job already to just ignore that. Think also about the not so obvious risk. If the AC-DC converter overheats and the insulation breaks down and the short circuit causes a fire, somebody might try to find the reason of the fire. And then you may face some hard time with your insurance.

Of course, all safety requirements have to be fulfilled by the final equipment assembly and the device is just a module. But the module is addressing makers and I guess not all of them do have the experience or education already to recognize the danger of improper insulation between primary and secondary circuitry.

This is version 1.0 of the device. From the pictures, it seems not to be too difficult to improve the design so that basic safety standards are fulfilled.
Until then, I would not recommend the device for people without suitable knowledge and experience.
And I would strongly recommend a related warning in big red letters in the product description.
(Posted on 9/20/2016)